Japanese patent No. 4853315 described below discloses a reinforced configuration in which a truncated conical through-hole is famed in a closed section member famed by coupling a first FRP member and a second FRP member, and a third truncated conical member made of FRP is stuck to an opening of the through-hole.
However, in the above-described prior art, since only a part of the third member was stuck to the first and second members, there was a problem that the reinforcing effect provided by sticking of the third member was not sufficiently exhibited.